Plating system for bone fixation and method of implantation

ABSTRACT

A modular bone distraction screw and a plate-based bone fixation device are well adapted for use in the spine. A plate has adjustable length and can accommodate bone settling. The method of use for each device is described and illustrated herein.

REFERENCE TO PRIORITY DOCUMENT

This application is a continuation of co-pending U.S. patent applicationSer. No. 11/025,659, entitled “Plating System for Bone Fixation andMethod of Implantation,” filed Dec. 28, 2004, which claims the benefitof priority of U.S. Provisional Patent Application Ser. No. 60/533,062,entitled “Plating System for Bone Fixation and Method of Implantation”,filed Dec. 29, 2003, U.S. Provisional Patent Application Ser. No.60/551,263, entitled “Plating System for Bone Fixation and Method ofImplantation, filed Mar. 8, 2004, and U.S. Provisional PatentApplication Ser. No. 60/603,808, entitled “Bone Fixation Plate andMethod of Implantation, filed Aug. 23, 2004. Priority of theaforementioned filing dates is hereby claimed, and the disclosures ofthe Applications indicated above are hereby incorporated by reference intheir entirety.

BACKGROUND

The present disclosure is directed at skeletal plating systems,components thereof, and method of implant placement. Such systems areused to adjust, align and maintain the spatial relationship(s) ofadjacent bones or bony fragments during healing and fusion. Such systemsmay be comprised of bone distraction devices, skeletal plates, bonescrews and/or bone cables, bone screw-to-plate locking mechanisms, andany additional instruments for implant placement.

Whether for degenerative disease, traumatic disruption, infection orneoplastic invasion, surgical reconstructions of the bony skeleton arecommon procedures in current medical practice. Regardless of anatomicalregion or the specifics of the reconstructive procedure, many surgeonsemploy an implantable skeletal plate to adjust, align and maintain thespatial relationship(s) of adjacent bones or bony fragments duringpostoperative healing. These plates are generally attached to the bonyelements using bone screws or similar fasteners and act to share theload and support the bone as osteosynthesis progresses.

Available plating systems used to fixate the cervical spine possessseveral shortcomings in both design and implantation protocols. Theseplates are manufactured and provided to the surgeon in a range of sizesthat vary by a fixed amount. This mandates that a large number ofdifferent size plates must be made and inventoried—adding to cost formanufacturer, vendor, and end user (e.g., hospitals). More importantly,the pre-manufactured sizes may not precisely fit all patients forcingsurgeons to choose between a size too small or too large.

Current cervical plates are not modular, and will not permit addition ofone plate to another for extension of the bony fusion at a future date.It is accepted that fusion of a specific spinal level will increase theload on, and the rate of degeneration of, the spinal segmentsimmediately above and below the fused level. As the number of spinalfusion operations have increased, so have the number of patients whorequire extension of their fusion to adjacent levels. Currently, theoriginal plate must be removed and replaced with a longer plate in orderto fixate the additional fusion segment. This surgical procedurenecessitates re-dissection through the prior, scarred operative fieldand substantially increases the operative risk to the patient. Further,since mis-alignment of the original plate along the vertical axis of thespine is common, proper implantation of the replacement plate oftenrequires that the new bone screws be placed in different bone holes. Theempty holes that result may act as stress concentration points withinthe vertebral bodies, as would any empty opening or crack within a rigidstructural member, and lead to bone fracture and subsequent screw/platemigration.

Current plates may provide fixation that is too rigid. Since bonere-absorption at the bone/graft interface is the first phase of bonehealing, fixation that is too rigid will not permit the bone fragmentsto settle and re-establish adequate contact after initial boneabsorption. This process is known as “stress shielding” and will lead toseparation of the bony fragments and significantly reduce the likelihoodof bony fusion. Unsuccessful bone fusion may lead to construct failureand will frequently necessitate surgical revision with a secondoperative procedure.

Benzel (U.S. Pat. Nos. 5,681,312, 5,713,900) and Foley (Pat. Applic.Pub. No. US2001/0047172A1) have independently proposed platting systemsdesigned to accommodate bone settling. In either system, however, bonysubsidence causes one end of the plate to migrate towards an adjacent,normal disc space. This is highly undesirable since, with progressivesubsidence, the plate may overly the disc space immediately above orbelow the fused segments and un-necessarily limit movement across anormal disc space. Clearly, accommodation of bone settling at theplate's end is a sub-optimal solution.

The implantation procedures of current plates have additionalshortcomings. Distraction screws are used during disc removal andsubsequent bone work and these screws are removed prior to bone plateplacement. The empty bone holes created by removal of the distractionscrews can interfere with proper placement of the bone screws used toanchor the plate and predispose to poor plate alignment along the longaxis of the spine. This is especially problematic since the surgicalsteps that precede plate placement will distort the anatomical landmarksrequired to ensure proper plate alignment, leaving the surgeons withlittle guidance during plate implantation. For these reasons, boneplates are frequently placed “crooked” in the vertical plane and oftenpredispose to improper bony alignment. Correct plate placement in thevertical plane is especially important in plates intended to accommodatebony subsidence, since the plate preferentially permits movement alongits long axis. Thus, when the vertical axis of the plate and that of thespine are not properly aligned, the plate will further worsen the bonyalignment as the vertebral bones subside.

The empty bone holes left by the removal of the distraction screws alsoact as stress concentration points within the vertebral bodies, as wouldany empty opening or crack within a rigid structural member, andpredispose them to bone fracture and subsequent screw/plate migration.Improper plate placement and bony fractures can significantly increasethe likelihood of construct failure and lead to severe chronic pain,neurological injury, and the need for surgical revision with a secondprocedure.

Yuan et al describes a multi-segmental plate consisting of two slidingparts in U.S. Pat. No. 5,616,142. While intended to be absorbable,Yuan's design permits excessive play between the sliding component andencourage bone screw loosening. In addition, this device does not permitapplication and maintenance of a compressive force across the bonyconstruct, as most surgeons prefer. Baccelli noted these deficiencies inU.S. Pat. No. 6,306,136 and proposed a rigid plate capable ofmaintaining bony compression. Unfortunately, the latter plate did notpermit subsidence.

SUMMARY

In view of the proceeding, there is a need for an improved bone platingsystem and placement protocol. Described herein is a modular bone plateof adjustable length that will accommodate bone settling. The deviceprovides ease of use, reliable bone fixation, adjustable length, modulardesign, and the ability to accommodate and control bone settling. Thedevice maximizes the likelihood of proper plate placement and avoidsmaneuvers that weaken the vertebral bodies.

In accordance with one aspect, a modular distraction screw is used forthe bone work prior to plate placement. The distraction screw is placedas the first step of surgery when all relevant landmarks are stillintact. After completion of the bone work, the proximal end of thedistraction screw is detached, leaving a distal segment still implantedin the vertebral bodies above and below the newly fused disc space. Theplate is guided to proper position along the upper and lower vertebra bythe attached distal segments. The distal segments of the distractionscrews are tightened onto the plate and the plate is held stationarywhile bone screws are placed.

The distal segments are used to guide the bone plate into the correctplacement position and serve to hold the plate stationary while theplate's bone screws are placed. Since the distraction screws were placedwith intact surgical landmarks, use of the distal segments to guide theplate significantly increases the likelihood of proper plate placement.In addition, this placement method allows the distal segments of thedistraction screws to serve as additional points of fixation for theplate and leaves no empty bone holes to serve as stress concentrationpoints and further weaken the vertebral bodies.

After the plate is attached to the upper and lower vertebras, the plateis set to the desired length and the locking element is deployed. If acompressive force across the vertebral bodies is desired, compression isapplied prior to deployment of the locking element. After deployment,the plate maintains the force across the vertebral bodies and permits apre-determined amount of bony subsidence. The plate does not overlap theadjacent disc space with bone subsidence, since movement is accommodatedat the level of settling bone and not at the plate's end. Moreover, theplate permits maintenance of a compression force as well asaccommodation and control of bony subsidence, among other features.

Extension of the fusion at a later date is easily accomplished withoutplate removal. An adapter is placed at either end of the plate to permitfusion extension. The procedure is started by connecting a modifieddistraction screw to the coupler at the end of the plate immediatelyadjacent to the disc to be fused. A modular distraction screw isinserted into the adjacent vertebra and a discectomy and subsequentfusion are performed within the intervening disc space. After completionof the bone work, the modified distraction screw is removed leaving thebare coupler on the end of the plate. The proximal segment of thedistraction screw is also removed leaving the distal segment attached tothe adjacent vertebral body. An extension plate is used to span thespace between the distal segment of the distraction screw on theadjacent vertebra and the end-coupler on the original plate. In thisway, the fusion is extended and the newly fused segment is fixatedwithout removal of the original plate.

In accordance with one aspect, there is disclosed a bone fixationdevice, comprising: a first member connectable to a first vertebra; asecond member connectable to a second vertebra and interconnected withthe first member, the first and second members being movable relative toone another; and at least one distraction screw interface configured tocouple to a distraction screw for temporarily immobilizing the bonefixation device relative to the first and second vertebra, wherein thedistraction screw couples to the distraction screw interface at aplurality of locations relative to the bone fixation device.

In accordance with another aspect, there is disclosed a bone fixationdevice for retaining bone structure in a desired spatial relationship,comprising: a first member connectable to a first bone structure; asecond member connectable to a second bone structure and interconnectedwith the first member, wherein the first and second members are movablerelative to one another across a range of motion; and a locking memberthat transitions between a first state wherein the locking memberengages the first member, and a second state wherein the locking memberengages the second member, wherein the locking member and the firstmember move in unison across a first distance when the locking member isin the first state, and wherein the locking member and the second membermove in unison across a second distance when the locking member is inthe second state.

In accordance with another aspect, there is disclosed a device forpositioning a bone fixation plate relative to a bone structure,comprising: a holder portion configured to be removably attached to thebone fixation plate; and an actuator coupled to the holder portion,wherein the actuator is actuated to move the holder portion to therebyadjust the size of the bone fixation plate.

The plating systems described herein provide ease of use, reliable bonefixation, adjustable length, modular design, and the ability toaccommodate and control bone settling. The plate maximizes thelikelihood of proper plate placement, avoid maneuvers that weaken thevertebral bodies, and provides a significant advantage over the priorart. These and other features will become more apparent from thefollowing description and certain modifications thereof when taken withthe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows various views of a modular distraction screw.

FIG. 2 shows the distraction screw in an assembled state such that adistal segment is coupled to a proximal segment.

FIG. 3 shows a distal section of the distraction screw.

FIG. 4 shows components of a proximal portion of the distraction screw.

FIG. 5 shows an enlarged view of the proximal portion coupled to thedistal portion of the distraction screw.

FIG. 6 shows various views of the interaction of an elongated body and adeployable member at the upper end of an assembled proximal segment ofthe distraction screw.

FIG. 7 illustrates how the assembled proximal segment couples to thedistal segment of a distraction screw.

FIGS. 8 and 9 shows perspective views of a bone fixation deviceconfigured to retain bone portions such as cervical vertebra of a spinalcolumn in a desired spatial relationship.

FIGS. 10A-10E illustrates various views of a sliding component of thedevice.

FIGS. 11A-11E illustrate various view of another sliding component ofthe device that couples to the sliding component shown in FIGS. 10A-10E.

FIGS. 12A-12D shows various views of a locking component of the device.

FIG. 13 shows the device in an assembled state.

FIGS. 14A and 14B shows a cross-sectional views of the device.

FIGS. 15A and 15B shows cross-sectional, perspective views of thedevice.

FIG. 16 illustrates an instrument used to hold a plate and guide it intoposition.

FIG. 17 shows a close-up view of the end of the instrument used tointeract with the plate.

FIG. 18 illustrates the holder coupled to and interacting with theplate.

FIG. 19 shows a close up view of the holder interacting with the plate.

FIG. 20 shows the holder being used to deliver a plate onto a bonestructure.

FIG. 21 shows a plate seated on a bone structure with the plate holderattached.

FIG. 22 shows a modular distraction screw engaging an end-coupler of aplate mounted on a bone structure.

FIG. 23 shows an offset modified distraction screw in conjunction with aplate mounted on a bone structure.

DETAILED DESCRIPTION

Disclosed is a modular bone distraction screw and a plate-based bonefixation device. While they may be used in any skeletal region, thesedevices are well adapted for use in the spine. Exemplary embodiments ofthe fixation device, distraction screw and the method of use aredescribed with respect to the spine region. The plate has adjustablelength and can accommodate bone settling. The method of use for eachdevice is described and illustrated herein.

Modular Distraction Screw

FIG. 1 shows various views of a modular distraction screw 10, which iscomprised of a distal segment 120 and a removable proximal segment 130coupled to the distal segment 120. The distal segment 120 has a headportion 122 and a threaded shank portion 124, which can be securelyfastened unto a body structure such as bone. The proximal segment 130 iscomprised of an elongated body 132 that is axially positioned within asheath-like deployable member 136. Elongated body 132 has twosmooth-walled external indentations 134 and deployable member 136 issituated within those indentations. Deployable member 136 is adapted tobe retractably deployed beyond the distal end of indentations 134. FIG.2 shows the distraction screw 10 in an assembled state such that thedistal segment 120 is coupled to the proximal segment 130.

FIG. 3 shows various views of distal segment 120 of the distractionscrew 10. Distal segment 120 is comprised of a threaded shank portion124 and a head portion 122. The threads can vary in configuration. Forexample, the threads can be self-tapping and/or self-drilling. Dependingon the particular application, the shank portion 124 can be of variablelengths and diameter and the threads can be of any design that issuitable for attachment onto bone.

As shown, an embodiment of head portion 122 is composed of at least twosegments, including first segment 123, which is rotationally positionedwithin second segment 125. The second segment 125 has two or moreprotrusions that limit the rotation of first segment 123. When aclockwise rotational force is applied to a central indentation 1222within first segment 123, the first segment 123 will rotate untilstopped by the interaction of protrusion 1224 and indentation 1226. Oncestopped, application of additional rotation will cause distal segment120 to exert force against the protrusions 1224, such that the entiredistal segment turns in unison, such as in a clock-wise fashion.Conversely, application of a counter clock-wise rotational force willreturn sub-segment 1220 to the closed position and further rotation willcause distal segment 120 to turn in unison in a counter clock-wisefashion.

The proximal segment 130 is now described in more detail with referenceto FIG. 4, which shows the elongated body 132 and the deployable member136 of the proximal segment. Upper and lower views of elongated body 132are shown on the left of FIG. 4 and deployable member 136 is showninteracting with distal segment 120 on the right (without body 132). Thedeployable member has a pair of arms 501 that couple to the head portion122 of the distal segment 120. FIG. 5 shows a close-up view of the arms501 that permit proximal segment 130 to lock onto distal segment 120. Asshown, the arms 501 are sized to couple to the head of the distalsegment. FIG. 6 shows the interaction of elongated body 132 anddeployable member 136 at the upper end of assembled proximal segment130. As shown, the upper end of the elongated body 132 has a tabconfiguration that mates with the upper end of the deployable member136. FIG. 7 illustrates how the assembled proximal segment 130 couplesto distal segment 120.

The coupled proximal segment 130 and distal segment 120 employing thepreviously described means of engagement provide a modular distractionscrew. When fully assembled, the screw will function as a unitarydevice. In a surgical application, a wrench (not shown) is attached tothe distraction screw and the distraction screw is positioned at a siteof a bone. A rotational force is applied to portion 180 (FIG. 1) ofelongated body 132 causing the proximal and distal segments to rotate inunison so that the threads of distal segment 120 engage the underlyingbone and shank 124 is advanced into the bone.

After the distraction screws are used to perform the bone work, proximalsegments 130 are detached. Each distraction screw is disassembled intoits components and a distal segment 120 is left attached each vertebralbody. The distal segment provides enhanced structural integrity of thebone by reducing the stress concentration generally expected of an emptyopening in a structural member. In addition, leaving the distal segment120 attached to bone eliminates the robust bone bleeding encounteredafter removal of current, commercially-available distraction screws andobviates the need to fill the empty hole with a hemostatic agent.

Each distal segment 120 also provides an anchor point for the skeletalplate and helps insure proper plate placement. Since placement of thedistraction screws is performed as the first step in the surgicalprocedure, the anatomical landmarks required to ensure proper alignmentof the plate in the desired anatomical plane are still intact.

Plate Device

FIGS. 8 and 9 shows perspective views of a bone fixation device 5configured to retain bone portions such as cervical vertebra of a spinalcolumn in a desired spatial relationship. FIG. 8 shows the device 5 inan exploded state and FIG. 9 shows the device 5 in an assembled state.The device 5 is preferably convex in both the vertical and horizontalplanes in order to conform to the shape of the anterior aspect of thevertebral bodies. Further, the plate surface immediately adjacent to thebone may contain one or more indentations (not shown) that permit theplacement of additional curvature.

With reference to FIGS. 8 and 9, the device 5 includes a first slidingcomponent 20, a second sliding component 110, and one or more lockingcomponents 30, which are described in more detail below. The slidingcomponent 20 includes one or more elongate rods 2101 that extend along alongitudinal direction. The device 5 further includes a plurality offasteners, such as bone screws, that can be used to fasten the slidingcomponent 20 and sliding component 110 to a bone such as to a cervicalvertebrae. The bone screws may be of any known design that isappropriate for fixation of and implantation into human bone.

After engaging the underlying bone, the screws may be further attachedto the plate using any of a variety of screw-to-plate lockingmechanisms. Such mechanisms include, but are not limited to, the methodsand devices illustrated in U.S. Pat. Nos. D440311S, D449692S, 5,364,399,554,612, 5,578,034, 5,676,666, 5,681,311, 5,735,853, 5,954,722,6,039,740, 6,152,927, 6,224,602, 6,235,034, 6,331,179, 6,454,769,6,599,290, 6,602,255, 6,602,256, 6,626,907, 6,652,525, 6,663,632, and6,695,846. It is understood that one of ordinary skill in the art canapply these or any other suitable screw retention system and method tothe plate devices described herein.

The components 20 and 30 are configured to slidingly move relative toone another. In one embodiment, the component 110 slides along elongaterods 2101 that extend from the sliding component 20 such that thecomponent 110 can slide along a span, or degree, of linear movement.Alternately, the rods 2101 can have a curvature to provide a curvedrange of movement. It should be appreciated that the rods 2101 can havea variety of cross-sectional shapes. For example, the rods 2101 areshown having a straight-lined cross-sectional shape, although thecross-sectional shape can be circular or oval.

The third component 40 can be manipulated to control the degree ofmovement that is allowed between the components 20 and 30. As describedbelow, the third component 40 can transition between two or more statesthat control the range of motion of the first component relative to thesecond component. An actuation member comprising a screw 21 can becoupled to the component 110 and the component 40 to transition thecomponent 40 between the two states. When the locking component is in anopen, or unlocked, state, the first and second components can moveacross a first range of motion relative to one another. When theadjustor component is in a closed, or locked, state, the first andsecond components can move across a second range of motion relative toone another. In one embodiment, the “range of motion” comprises linearand sliding movement that spans a predetermined distance. The linearmovement can be in the longitudinal direction, which corresponds to thelongitudinal axis of the spinal column. In one embodiment, the range ofmotion is a non-zero value both when the component 40 is in the unlockedor locked state. However, it should be appreciated that the range ofmotion does not have to be a non-zero value.

Each of the components 20 and 30 of the device 5 includes at least onebone screw interface, such as one or more boreholes, that can receive orthat can matingly engage with a distraction screw, as described below.The borehole permits an additional distraction screw to be attached tothe underlying vertebra and/or the device 5 without removing the device5 from the vertebra.

The device 5 includes a modular aspect that permits the device 5 to bemodularly attached to a second device, such as, for example, a couplerto a second bone fixation device, while the device 5 is attached to aspine. The device 5 does not have to be removed from the spine in orderto modularly attach the second device to the device 5 in a modularfashion. It should be appreciated that the second device can be a deviceother than a bone fixation device. When the second device is coupled toa bone fixation device, the modular attachability allows a bone graft tobe extended to additional vertebrae without having to remove theoriginal bone fixation device.

FIGS. 10A-10E illustrates various views of sliding component 110, whichhas two boreholes 1110 which are angled towards each other in thehorizontal plane and away from the sliding end in the vertical plane.The boreholes 110 are configured to receive a bone screw that can beused to attach the component 110 to an underlying bone structure. Adepression 1120 is present between boreholes 1110 with an elongatedchannel 1130 within that depression. A wall is situated between the topof channel 1130 and the opening of depression 1120. The wall is angledrelative to the horizontal plane.

The channel 1130 is configured to receive a distraction screw, such as,for example, the modular distractions screw described herein or othertype of distraction screw. Advantageously, the channel 1130 is shapedsuch that the distraction screw can be positioned at various locationsalong the channel 1130, thereby permitting a variable distance betweenthe distraction screw and the bone screws positioned in the boreholes110. Thus, if the distraction screw is used to immobilize the plateduring bone screw placement, the position of the plate prior to bonescrew placement can be adjusted by moving the plate relative to thedistraction screw.

Some existing bone fixation plates have an indentation along the plateborder and use conventional, non-modular distraction screws toimmobilize the plate during bone screw placement. Since the distractionscrews make contact with the plate at fixed region of the plate, thedistraction screws can only fixate the plate when they're tightly fittedagainst it. This mandates that the bone screw center must be placed aconstant distance from the center of the distraction screw in thevertical plane.

A fixed spatial relationship between the bone screw and distractionscrew is highly undesirable. Since bone spur formation obscures the trueposition of the vertebral end plate at the time of distraction screwplacement, bone screw placement that is based on the position of thedistraction screw will significantly increase the likelihood of improperplate placement.

In order to ensure proper plate placement, the surgeon must be able toadjustment the plate's position in the vertical plane. In the devicesdescribed herein, after the optimum position is selected, thedistraction screws can be used to immobilize the plate and the bonescrews is then placed. This strategy is most effectively accomplished byusing a slot between the bone screw holes as in the current device.

With reference still to FIGS. 10A-10E, the component 110 includes asliding mechanism comprising a pair of longitudinally-extending rodshafts 355 that extend through the component 110. The rod shafts 355 aresized to receive a corresponding rod 2101 of the component 20, asdescribed below. In this regard, each of the rod shafts 355 ispositioned so as to be axially aligned with the corresponding pair ofrods 2101 of the component 20 and has a shape configured to receive arespective rod shaft. In one embodiment, the rods 2101 are configured toengage with the component 30 in a manner that minimizes the likelihoodof the rods 2101 disengaging therefrom. In this regard, the end portionsof the rods can have a size that is slightly larger than the entrydiameter of the rod shafts 355 so that once the rods 2101 are positionedin the rod shafts, the enlarged diameter prevents the rods 2101 frominadvertently moving out of the shafts.

The component 110 includes a central shaft or indentation 116 (FIG.10D). An opening 1162 is situated within the top surface of indentation116. A vertical hole 118 has threads, rests next to central indentation116 and opens onto indentation 116 through an opening. The hole 118 issized to receive the screw 21.

The end opposite to the sliding mechanism has an end-coupler 120 with acentral hole 1202. A relief is cut along a wall of the hole 1202 to aidin the attached of any add-on devices. While depicted as acircumferential channel, the relief may be of any appropriate geometricshape that complements the add-on device. Further, the inside wall ofhole 1202 may contain additional indentations, spines or texture toincrease frictional contact between the plate and add-on devices.

FIGS. 11A-11E illustrate the complementary sliding component 20. Again,two boreholes 210 are present and angled towards each other in thehorizontal plane and away from the sliding end in the vertical plane.Each of the boreholes 210 is sized to receive a corresponding fastenerscrew. In one embodiment, a screw head engagement structure, such as anannular lip or shelf, is located within each borehole 210. The head of afastener screw can engage the shelf and provide a fastening forcethereto during fastening of the component 20 to a vertebra. In theillustrated embodiment, the component 20 has two boreholes 210, eachlocated near a transverse side of the main body. The boreholes 210 canbe aligned with an axis that is oriented in the true vertical plane, orthe axis can form an angle with the vertical. For use in the cervicalspine, boreholes 210 can be angled towards each other in the horizontalplane and away from the rods 2101 in the vertical plane. The top openingof the boreholes 210 may be flush with the outer surface, can be curved,or can be further recessed so as to form the shelf 315.

A depression is present between the boreholes 210 with an elongatedchannel 210 positioned between the boreholes 210. A wall is situatedbetween the top of channel 230 and depression 220 and it is angled withthe true vertical.

As mentioned, the sliding end of component 20 includes a pair of rods2101 and a central projection 250. The rods 2101 are sized to beinserted into the channels 355 in the component 110 and the centralprojection is sized to be inserted into the indentation 116. The ends ofthe rods 2101 have additional projections that lock the plate togetherso that once assembled it can not be pulled into its individualcomponents. Likewise, the central projection 250 complements withindentation 116 of component 110. An end coupler 270 is located at thean opposite end of component 20 and may contain additional indentations,spines and texture—as described for end-coupler 120.

FIGS. 12A-12D illustrates various views of the locking element 30. Thelocking element includes a plate portion 1181 that is sized and shapedto be received into the indentation 116 along with the centralprojection 250 of the component 20. A raised region 1183 protrudes intothe opening 1162 in the component 20 when the device is assembled. Thelocking element 30 further includes a retractable side-arm 320. Theside-arm 320 fits within opening 1182 of component 110 and an inneraspect of arm 320 is preferentially textured or slotted to increasefictional contact with other segments. That is, the side-arm 320 extendsthrough the opening 1182 in the side of the hole 118 of the component110 when the device 5 is assembled.

FIG. 13 shows the device 5 in an assembled state. The rods 2101 ofcomponent 20 are slidingly coupled to the component 110. The lockingelement 30 is positioned between the components 20 and 110 such that theraised region 1183 protrudes through the opening 1162. The raised region1183 can slide within the opening 1162 along a distance L.

The screw 21 can be moved between an open and closed state to transitionthe side-arm 320 of the locking element between an open state and aclosed state. When the side arm is in the open state, the lockingcomponent 30 and the component 20 cannot move relative to one another,but rather move as a unitary component.

This is described in more detail with reference to FIGS. 14A, 14B, 15A,and 15B. FIGS. 14A and 15A shows the screw 21 and the locking element 30in an open state. With screw 21 open, side-arm 320 sits within opening1182. The side arm 320 thereby engages the component 110 so that lockingelement 30 and component 110 can not move relative to one another.However, component 20 can slide freely relative to element 30 andcomponent 110 along the length of the rods 2101.

However, when screw 21 is locked and fully seated within hole 118 (asshown in FIGS. 14B and 15B), the screw 21 pushes the side-arm 320 out ofthe opening 1182. This causes the interior aspect of the side arm 320 toengage the projection 250. As mentioned, the side arm 320 can have atextured surface that makes contact with the side of projection 250 ofcomponent 20. Thus, with screw 21 locked, the side arm 320 of thelocking component 30 engages the projection 250 of component 20 and bothpieces (components 20 and 30) move in unison within opening 1162 ofcomponent 110. The extent of such movement is limited by the length L(FIG. 13) of opening 1162. In this way, when screw 21 is open, component110 and locking element 30 move in unison relative to component 20 andprovide a plate of variable length. With screw 21 closed, component 20and locking element 30 move in unison within opening 1162 of component110 permitting accommodation of bone subsidence.

Placement Protocol

Modular distraction screws are placed into the vertebral bodies aboveand below the disc to be removed as previously described. A discectomyis performed and the evacuated disc space is fused. After the bone workis complete, the screws are disassembled leaving the distal segmentsattached to the vertebral bodies. The distance between the distalsegments is measured and a plate of appropriate size is selected. Sincea sliding plate can accommodate a range of sizes, choosing the correctplate size is simplified when a sliding plate design is used.

While the preferred method of plate placement utilizes modulardistraction screws, the plate may be also implanted without them. Forexample, a conventional one-piece distraction can be used to distractthe vertebra during discectomy. After the bone work is finished, theconventional distraction screw is removed. Distal segments 120 areplaced into the vertebral bodies and provide anchor points for theskeletal plate. As discussed, the plates have channels that interfacewith the distraction screw along a plurality of locations such that therelative positions between the distraction screws and the bone screwscan be varied during placement. Alternatively, the plate may be manuallyheld stationary while the bone screws are placed.

FIG. 16 illustrates a holder instrument used to hold the plate and guideit into position. FIG. 17 shows a close-up view of the end of theinstrument used to interact with the plate. The holder instrumentincludes a holder member that is configured to couple to the plate. Inparticular, the holder portion includes a first attachment member thatremovably attaches to the first component and a second attachment memberthat removable attaches to the second component of the plate device. Inone embodiment, the attachment members are sized and shaped to beinserted into a portion of the respective components, such as into theboreholes. FIG. 18 illustrates the holder coupled to and interactingwith the plate. FIG. 19 shows a close up view of the holder interactingwith the plate.

With movement of the holder's handle, the plate opens and closes. Inparticular, the holder 1901 has an actuator handle 1906 and a holdermember 1910 (previously described) that couples to the plate device 5.The actuator handle 1906 is actuated to cause the first and secondattachment members to move relative to one another. In this manner, theactuator handle 1906 can be actuated to move the first and secondmembers relative to one another and thereby adjust the size of thedevice. In one embodiment, the actuator handle can be actuated using asingle hand, thereby freeing the other hand for other tasks. A rack andpinion configuration can be employed to transfer movement of the handleto the attachment members of the holder. However, it should beappreciated that other mechanisms can be used.

FIG. 20 shows the holder instrument being used to deliver a plate onto abone structure. As illustrated in FIG. 20, the plate 5 is brought intothe wound and component 110 is guided onto head 122 of distal segment120 of the modular distraction screw anchored in one vertebra V1. Theother end of the plate 5 is guided onto the distal segment 120 anchoredin the other vertebra V2 component 20 is lowered onto it. FIG. 21 showsplate seated on the bone structure with plate holder 1910 attached. Atthis point, the plate's boreholes 110 are moved (relative to thevertebral bodies V1, V2) into optimal position for bone screw placement.After positioning the plate, a screw driver is used to turn distalsegment 120 clock-wise, thereby opening the head of the distal segment.Additional turns of the screw will drive the distal segment further intothe bone and hold the plate between the screw head and the underlyingbone.

With both distal segments locked, the plate is held stationary and thebone screws are easily placed into the underlying bone. Note that thesegment of the holder adjacent to the plate's bore holes will also serveas guide for proper screw (and drill, for non-self drilling screws)placement. Bone screws and plate-to-screw locking mechanisms of anyappropriate design may be employed. Compression may be added across theconstruct using plate holder. Screw 21 is closed thereby locking plateat the set length and maintaining any compression provided. At thispoint, components 20 and 110 can still move towards each other,permitting accommodation of bone settling. As mentioned, the extent ofsubsidence permitted is governed by the length of opening 1162.

Extension of the fusion at a future date can be accomplished withoutplate removal. Incorporation of the vertebral body immediately above orbelow into the fusion mass is started by placement of a modulardistraction screw into the adjacent vertebra. A modified distractionscrew is used to engage the end-coupler of the existing plate as shownin FIG. 22. The modified distraction screw is formed by an elongatedbody 510 with an internal bore 512 extending through its entire length.The elongated body 510 houses a deployable member 530, which is disposedwithin the internal bore 512. Threads 532 are located on one end ofmember 530 and head 534 is located on the other end. A depression 536 isformed within head 534 so as to permit engagement and rotation ofdeployable member 530 with a complimentary screwdriver.

When the discectomy and subsequent bone work are finished, the modulardistraction screw is separated leaving the distal segment attached tovertebral body. The modified distraction screw is removed. A separateplate is used to span the distance between the distal segment 120attached to the adjacent vertebra and the end coupler of the plate. Inthis way, the fusion is extended to an adjacent level without removal ofthe existing plate.

Occasionally, the end coupler of the plate abuts the adjacent disc spacesuch that placement of the modified distraction screw onto the couplerhinders surgical access to the disc space. FIG. 23 shows an offsetmodified distraction screw which may be used in this setting. The screwcomponents are similar to those described above for the non-offsetscrew.

Although embodiments of various methods and devices are described hereinin detail with reference to certain versions, it should be appreciatedthat other versions, embodiments, methods of use, and combinationsthereof are also possible. Therefore the spirit and scope of theappended claims should not be limited to the description of theembodiments contained herein.

1. A device for positioning a bone fixation plate relative to a bonestructure, comprising: a holder portion configured to be removablyattached to the bone fixation plate; an actuator coupled to the holderportion, wherein the actuator is actuated to move the holder portion tothereby adjust the size of the bone fixation plate.
 2. A device as inclaim 1, wherein the holder portion comprises a first holder memberconfigured to removably attach to a first component of the bone fixationplate, and a second holder member configured to removably attach to asecond component of the bone fixation plate, and wherein actuation ofthe actuator moves the first holder member relative to the second holdermember to thereby slidably move the first component relative to thesecond component.
 3. A device as in claim 2, wherein the first holdermember is sized to be removably inserted into a portion of the firstcomponent and wherein the second holder member is sized to be removablyinserted in a portion of the second component.
 4. A device as in claim1, wherein the actuator member is positioned in a handle of the device.5. A device as in claim 4, wherein the actuator member is configured tobe actuated using a single hand.